Recently, with the widespread use of the Internet and e-mailing, information processing devices such as a personal computer and a PDA (Personal Digital Assistant) have been used among users of all ages. Keyboards of these information processing devices in general, use a same key arrangement of mechanical typewriters having been popular in the past. However, the key arrangement is not necessarily suitable to the structure of hands, arms, and elbows of a person and recently there arises a problem of inflammation of the tendon sheath and mental stress due to typing for long hours.
Regarding this problem, Japanese Laid-open Patent Publication No. H09-73347 describes a technique of opening a front side of a folding keyboard made up of a right side segment and a left side segment for use, to separate the right side segment and the left side segment from each other. According to this folding keyboard, plural keys are diagonally arranged in the shape of a V-letter when opened for use, enabling a user to use the keyboard with the arms naturally opened, thereby reducing loads on the shoulder and the elbows of the user.
However, although the above-described folding type keyboard may be able to reduce physical burdens when operating the keyboard with both hands, there is a problem that the shoulder and the arms need to be moved extensively similarly to conventional keyboards, when operating the keyboard with only one hand. Additionally, since the Shift key and the Control key that are pressed together with another key are arranged at both ends in a width direction of the keyboard, operating the conventional type keyboard with one hand is difficult. Further, moving the hand in the width direction of the keyboard is burdensome compared to moving in a depth direction thereof, therefore it is necessary to narrow the width of the keyboard to operate the keyboard with one hand. As a means for narrowing the width of the keyboard, it is conceivable to downsize keys of the keyboard by narrowing a distance between adjacent keys (key pitch) and to arrange keys so as to make the depth direction of the keyboard become a longitudinal direction.
However, downsizing the keys raises a problem of poor operability since an extra key may be often pressed together unintentionally. And for a user accustomed to the traditional QWERTY arrangement that has been widely employed, it is uncomfortable to use the keys that are arranged long in the depth direction of the keyboard. Recently, it is often the case where the keyboard is operated with one hand not only by handicapped users, but also by users holding a receiver or reference materials. In such a case, currently a mouse is often used and there is a demand for developing a keyboard with excellent key operation with one hand.